It is known in the art of motor drive circuits to use a current regulator (or current controller) to control motor current. It is also known to use proportional-plus-integral (P-I) closed loop control of motor current to provide synchronous control of motor currents. However, such current regulator must be accurately tuned to the electromagnetic dynamics of the motor to provide precise control of motor currents and, therefore, precise control of torque generated at the motor shaft. In particular, for a P-I controller, the proportional gain K.sub.P and the integral gain K.sub.I should be matched to the motor dynamics to provide optimal performance.
One technique to accurately determine such control parameters is to analyze the motor/drive system in an engineering laboratory using expensive test equipment and several engineering man-hours. However, in modernization or retrofit applications, where a new drive replaces an older drive in an existing elevator system, it is not convenient or cost effective to remove the motor from the elevator system for evaluation of the control parameters.
Another technique to determine the regulator control parameters involves dispatching a highly skilled engineer to the job site to tune the drive to the motor using special test equipment. However, such a technique is costly and time consuming and, as such, makes modernizing elevator motor drives unattractive for building owners.
Also, various techniques have been described for tuning current regulators, such as is described in: A. M. Khambadkone, et al, "Vector-controlled induction motor drive with self-commissioning scheme", IEEE Trans. Ind. Electronics, Vol. 38, No. 5, October 1991, pp. 322-327; H. Schierling, "Self-commissioning--a novel feature of modern inverter-fed induction motor drives", 3.sup.rd Int'l Conference On Power Electronics and Variable Speed Drives, IEEE Conf. Pub. No. 291, pp. 287-290; M. Summer, et al, "Autocommissioning for voltage-referenced voltage-fed vector-controlled induction motor drives", IEEE Proceedings-B, Vol. 140, No. 3, May 1993; and T. Kudor, et al, "Self-Commissioning for vector-controlled induction motors", IEEE Pub. ID# 0-7803-x/93, pp. 528-535.
Such techniques attempt to measure the motor parameters and then calculate current regulator gains according to an algorithm based on those estimates. In particular, Khambadkone and Schierling teach applying voltage pulses to the motor, and use the rate of rise of current to estimate the motor transient inductance. Summer teaches applying a pseudo-random binary sequence of voltage pulses to the motor and uses a recursive least-squares calculation to estimate the motor parameters. The current regulator parameters are determined by a pole-placement algorithm using the estimated motor parameters. Kudor teaches applying a step input to the current regulator, and computes a performance index based on step response. Fuzzy logic rules are employed to adjust the regulator gains to achieve optimum tuning. However, the foregoing techniques are costly and complex to implement.